Use of amine blends for foundry shaped cores and casting metals

ABSTRACT

The present invention relates to an improved process for preparing foundry shapes by the cold box process, a process for making cores and moulds and a process for casting metals, carrying out as curing catalyst system a blend comprising at least two tertiary amines.

This invention relates to the use of amine blends as curing agents forbinder compositions useful in the foundry art for making cores thatharden at room temperature. It also relates to combinations of foundryaggregates, such as sand and binder, generally based on phenolic (phenolaldehyde) resins and poly-isocyanates, which, on being formed into acoherent mass with the aggregate in a mould, generally a steel mould, iscapable of being cured at room temperature by an amine blend used ascuring agent. The self-supported cores as obtained can be used in makingmetal castings.

When the cured resins are based on both phenolic resins andpolyisocyanates, the above process utilized in foundries is namedPolyurethane Cold Box Process (PUCB).

According to this method, a two-component polyurethane binder system isused for the bonding of sand. The first component consists in a solutionof at least one polyol, generally comprising at least two OH groups permolecule. The second component is a solution of at least one isocyanatehaving at least two NCO groups per molecule.

The use of tertiary amines as curing agents has long been known in PUCB:see for example U.S. Pat. No. 3,429,848; U.S. Pat. No. 3,485,797; U.S.Pat. No. 3,676,392; and U.S. Pat. No. 3,432,457. Such tertiary aminesare sometimes utilized with metal salts and provide a fast curing ofphenol formaldehyde and poly-isocyanate resins at room temperature. Theycan be added to the binder system before the moulding stage, in order tobring the two components to reaction (U.S. Pat. No. 3,676,392) or theycan pass in a gaseous form through a shaped mixture of an aggregate andthe binder (U.S. Pat. No. 3,409,579).

Generally phenolic resins are used as polyols, which are preparedthrough condensation of phenol with aldehydes, preferably formaldehyde,in the liquid phase, at temperatures of up to around 130° C., in thepresence of divalent metal catalysts. The manufacture of such phenolicresins is described in detail in U.S. Pat. No. 3,485,797. In addition tounsubstituted phenol, substituted phenols, especially o-cresol andp-nonylphenol, can be used (see for example EP-A-0 183 782).

As additional reaction components, according to EP-B-0 177 871,aliphatic monoalcohols with one to eight carbon atoms can be used toprepare alkoxylated phenolic resins. According to this patent, the useof alkoxylated phenolic resins in the binder results in binders thathave a higher thermal stability.

As solvents for the phenolic components, mixtures of high-boiling pointpolar solvents (for example, esters and ketones) and high boiling pointaromatic hydrocarbons are typically used.

Preferred tertiary amines (catalyst) used in curing polyurethane coldbox (PUCB) processes are trimethyl amine (TMA), dimethyl ethyl amine(DMEA), dimethyl iso-propylamine (DMIPA), dimethyl-n-propylamine (DMPA)and triethyl amine (TEA). All these tertiary amines are taught in theart to be used individually.

The catalyst is usually introduced as a combination of one inert gas andone amine, in the liquid or gaseous state. The boiling point of theamine is preferably below 100° C. to permit evaporation and to achievesatisfactory concentration of amine in the amine-inert gas mixtureinjected into the steel mould. A boiling point below 100° C. also helpsto avoid condensation of the amine when it contacts the steel moulds.

However, the boiling point of the amine must be preferably high enoughto facilitate handling of the amine. Trimethylamine (TMA) is a gas atnormal ambient temperature (boiling point (Bp) 2.87° C.), which makes itdifficult to handle. Other drawbacks can be found with low boilingtertiary amines: the well-known low boiling tertiary amine DMEA (Bp 37°C.) has undesirable organoleptic characteristics. In particular, it hasa strong ammonia odor. Furthermore, this amine is very easilyimpregnated into skin and clothing, making a very unpleasant workingenvironment when it is used.

On the other hand, the 89° C. boiling point of triethylamine (TEA) isprobably the highest practical boiling point because TEA tends tocondensate out of the gas mixture in the piping which carries theamine-inert gas mixture to the steel mould in winter, and in additionbadly cured spots are found in sand cores produced in the steel mould.

The molecular weight of the amine must be low enough to permit readydiffusion of the amine through sand in the steel mould, especially inthe corners and edges of the mold. TEA, with molecular weight of 101, isprobably the highest molecular weight amine permissible for theso-called Cold Process; it has a very low odor intensity and very lowamine smell but displays lower curing ability than the tertiary amineswith lower molecular weights (Mw) and boiling points.

On an industrial point of view, tertiary amines containing 5 carbonatoms such as DMIPA (Mw 87, Bp 67° C.) or DMPA (Mw 87, Bp 65-68° C.) orDEMA (Mw 87, Bp 65° C.) constitute good compromise tertiary amines inthe field of catalytic gassing agents for curing resins in cold boxprocesses. Tertiary amines containing 5 carbon atoms require less energyinput and lower gassing temperatures in PUCB equipment than TEA.

DMIPA has a better reactivity than TEA: 1 kg of DMIPA is capable ofcuring approximately 1200 kg of sand/resin mixture, whereas 1 kg of TEAis capable of curing only 900 kg of the same sand/resin mixture. DMIPAis less odorant than the lighter tertiary amine DMEA.

Despite all these known curing amine catalysts, there is still a need toprovide an improved catalysis to the cold box process, i.e a catalystwhich hardens binding resins more quickly than tertiary aminescontaining 5 or more carbons, and which does not possess the strong,irritating, and itching ammonia odor associated with tertiary aminescontaining 4 or 3 carbons such as dimethylethylamine (DMEA) ortrimethylamine (TMA).

The present invention therefore relates to a new type of amine catalystfor cold box processes, said catalyst allowing a modulation ofreactivity and safer and easier handling during use.

More precisely, the present invention first relates to the use of ablend of at least two tertiary amines as catalyst for curing a compositeresin composition, especially for preparing a foundry shape by the saidcold box process.

The use of the present invention has many advantages, among other alower amount of the used curing blend of amines as compared to theamount theoretically expected, and allows a modulation of bothproperties of curing kinetics and safer handling and storage (lessodorant and less flammable catalyst), as compared to the known catalystsused in the art, which only consist in one single amine.

More particularly, the curing catalyst system used in the presentinvention is a blend of at least two tertiary amines, each displayingcuring reactivity and/or odor difference from one another. The blends ofamines used in the invention allow a modulation in reactivity.

Preferably the blend does not contain two C5 tertiary amines. However,two C₅ tertiary amines mixed with one or more C₃, C4 and/or C₆-C₁₀amines are encompassed in the present invention.

Generally, the blend comprises from 10 to 90 parts by weight of any ofthe amines present in the catalytic mixture. Advantageously, each amineis present in the blend in an amount of not less than 10% by weight, andnot more than 90% by weight.

Unless otherwise specified all percentages values in the presentdescription and claims are understood to be % by weight.

The blend according to the use of the present invention is preferably amixture of at least one tertiary amine having 3 to 5 carbon atoms withat least one tertiary amine having 6 to 10 carbons. Each tertiary aminegenerally is a trialkylamine, each alkyl group being linear, branched orcyclic, and two alkyl groups possibly forming, together with thenitrogen atom to which they are bonded, a cyclic group containing 2 to 9carbon atoms, preferably 2 to 6 carbon atoms. The invention does notexclude tertiary amines that contain a second, third or even fourthtertiary nitrogen atom.

The tertiary amines used in the invention may be substituted withfunctional groups, which do not interfere in the catalytic action of thetertiary amines. As substitution functional groups of the tertiaryamines, mention may be made for example of hydroxyl groups, alkoxygroups, amino and alkyl amino groups, ketoxy groups, thio groups, silylgroups and the like.

All tertiary amines used in the present invention are known,commercially available compounds, or may be easily prepared according toknown processes, or directly or indirectly from processes disclosed inthe scientific literature, patents, in the Chemical Abstracts or on theInternet.

According to a preferred embodiment, the blends comprise at least oneamine having a low molecular weight with at least one amine of highermolecular weight.

According to another embodiment, preferred blends comprise at least oneamine having a low boiling point with at least one amine of higherboiling point.

According to still another embodiment, preferred blends comprise atleast one fast curing tertiary amine with at least one less reactivetertiary amine.

In another embodiment, preferred blends comprise at least a fast curingtertiary amine having a low molecular weight and a low boiling pointwith at least a less reactive tertiary amine of higher molecular weightand higher boiling point.

Through the use of such blends, curing of polyurethane binder is lessodorant and safer to handle and store, than when a fast curing amine isapplied alone, and faster and more complete than with the use of a highboiling tertiary amine alone.

Examples of C₃-C₆ amines that can be used in the present inventioncomprise:

-   -   C₃ amines: trimethylamine, N-methylaziridine;    -   C₄ amines: dimethylethylamine (DMEA), N-methylazetidine,        N-ethylaziridine,    -   C₅ amines: diethylmethylamine (DEMA), dimethylisopropylamine        (DMIPA), dimethyl-n-propylamine (DMPA), N-n-propylaziridine,        N-iso-propylaziridine, N-ethylazetidine, N-methylpyrrolidine,        N,N,N′,N′-tetramethyl diamino methane,    -   C₆ amines: triethylamine (TEA), methylethyl-n-propylamine,        methylethyl-iso-propylamine, dimethyl-n-butylamine,        dimethyl-sec-butylamine, dimethyl-iso-butylamine,        dimethyl-tert-butylamine, N-ethylpyrrolidine,        N-methylpiperidine, hexamethylene tetramine, dimethyl        piperazine, N,N,N′,N′-tetramethyl diamino ethane,    -   C₇ amines: dimethylpentylamines, methylethylbutylamines,        diethylpropylamines, dipropylmethylamines, N-propylpyrrolidines,        N-ethylpiperidine,    -   C₈ amines: dimethylhexylamines, methylethylpentylamines,        diethylbutylamines, dipropylethylamines, N-butylpyrrolidines,        N-propylpiperidines, diethyl piperazine,    -   C₉ amines: dimethylheptylamines, methylethylhexylamines,        diethylpentylamines, tripropylamines, N-pentylpyrrolidines,        N-butylpiperidines,    -   C₁₀ amines: dimethyloctylamines, methylethylheptylamines,        diethylhexylamines, ethylpropylpentylamines,        dipropylbutylamines, N-pentylpiperidines.

Preferred amines for use in the blends according to the presentinvention are DMEA, DMIPA, DEMA, DMPA and TEA.

Examples of preferred blends of tertiary amines for use in the presentinvention are: DMEA-DMIPA, DMEA-DEMA, DMEA/DMPA and DMEA-TEA. Preferredblends are (weight ratios): 50/50 DMEA/DMIPA, 20/80 DMEA/DMIPA, 10/90DMEA/DMIPA, 50/50 DMEA/DMPA, 20/80 DMEA/DMPA, 10/90 DMEA/DMPA, 50/50DMEA/DEMA, 20/80 DMEA/DEMA, 10/90 DMEA/DEMA, 50/50 DMEA/TEA, 20/80DMEA/TEA, 10/90 DMEA/TEA, 80/20 DMEA/TEA and 90/10 DMEA/TEA, preferably20/80 DMEA/DMIPA, 20/80 DMEA/TEA and 80/20 DMEA/TEA. Preferably, theblend contains from 10 to 30 parts by weight of DMEA.

Such blends lead to improved curing efficiency as compared to theperformance of the highest boiling amine in the catalytic mixture forpolyurethane cold box curing and for odor improvement as compared to theodor carried by the lowest boiling component, if used alone.

Unexpectedly, blends of DMEA-DEMA and blends of DMEA-TEA, thecomposition of which preferably ranges from 10% to 50% by weight of DMEAto the total of the amine blend, display a synergy at curing; thiscuring synergy can be appreciated by measuring the global amount ofamines blend needed for a 100% curing of a sand+binder mixture versusthe theoretical amount of blend that is expected by adding the optimizedvolumes for each amine modulated by their abundance ratio in the blend.

Such a behavior is particularly advantageous because it allows not onlya better and immediate volatile organic compounds (VOC) reduction ascompared to other curing systems which do not display such a synergy,but also presents other advantages such as a faster curing than the oneobtained with a high boiling and high molecular weight tertiary aminewhen used as single curing catalyst, and less pungent and clotheimpregnating than the one obtained with a low boiling and low molecularweight tertiary amine when used as single curing catalyst.

Tertiary amine blends may be used in a liquid state or preferably in agaseous state and in any desired predetermined concentration, alone orpreferably in combination with an inert carrier.

The inert gaseous carrier can be nitrogen or air, but carbon dioxide,less expensive than nitrogen, is sometimes utilized.

It would not be outside the scope of the invention to use a mixturecomprising, in addition to the tertiary amines blend, up to 25%, andpreferably up to 10% by weight (to the total weight of all aminespresent in the blend) of at least one other, primary and/or secondaryamine. However, the amount of primary and/or secondary amine in theamine blend is more preferably maintained at 0.5% by weight or less.

The tertiary amine blend can also comprise small amounts of water: theconcentration of water in the blend is preferably kept below 0.2% byweight.

The present invention also relates to a process for preparing a foundryshape by the cold box process.

This process invention has many advantages, among other a lower amountof the used curing blend of amines as compared to the amounttheoretically expected, and allows a modulation of both properties ofcuring kinetics and safer handling and storage (less odorant and lessflammable catalyst), as compared to the known catalysts used in the art,which only consist in one single amine.

The invention thus relates to a process for preparing a foundry shape bythe cold box process, which process comprises the following steps:

-   -   (a) forming a foundry mix with the binder and an aggregate,    -   (b) forming a foundry shape by introducing the foundry mix        obtained from step (a) into a pattern,    -   (c) contacting the shaped foundry mix with a curing catalyst        comprising a blend of at least two tertiary amines, in a liquid        or preferably in a gaseous form, optionally with an inert        carrier,    -   (d) hardening the aggregate-resins mix into a hard, solid, cured        shape, and    -   (e) removing the hardened foundry shape of step (d) from the        pattern.

The binder system comprises at least one phenolic resin component and atleast one isocyanate component.

Phenolic resins are most generally manufactured by condensation ofphenols and aldehydes (Ullmann's Encyclopedia of Industrial Chemistry,Bd. A19, pages 371 ff, 5th, edition, VCH Publishing House, Weinheim).Substituted phenols and mixtures thereof can also be used. Allconventionally used substituted phenols are suitable.

The phenolic binders are preferably not substituted, either in bothortho-positions or in one ortho- and in the para-position, in order toenable the polymerization. The remaining ring sites may be substituted.There is no particular limitation on the choice of the substituent, aslong as the substituent does not negatively influence the polymerizationof the phenol and the aldehyde.

Examples of substituted phenols are alkyl-substituted phenols,aryl-substituted phenols, cycloalkyl-substituted phenols,alkenyl-substituted phenols, alkoxy-substituted phenols,aryloxy-substituted phenols and halogen-substituted phenols.

The above named substituents have 1 to 26, and preferably 1 to 12,carbon atoms. Examples of suitable phenols, in addition to theespecially preferred unsubstituted phenols, are o-cresol, m-cresol,p-cresol, 3,5-xylol, 3,4-xylol, 3,4,5-trimethyl phenol, 3-ethylphenol,3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol,cyclohexylphenol, p-octylphenol, 3,5-dicyclohexylphenol, p-crotylphenol,p-phenylphenol, 3,5-dimethoxyphenol, 3,4,5-trimethoxyphenol,p-ethoxyphenol, p-butoxyphenol, 3-methyl-4-methoxyphenol, andp-phenoxyphenol. Especially preferred is phenol itself.

All aldehydes, which are traditionally used for the manufacture ofphenolic resins, can be used within the scope of the invention. Examplesof these are formaldehyde, acetaldehyde, propionaldehyde,furfuraldehyde, and benzaldehyde.

Preferably, the aldehydes commonly used should have the general formulaR′CHO, where R′ is hydrogen or a hydrocarbon radical with 1-8 carbonatoms. Particularly preferred is formaldehyde, either in its dilutedaqueous form or as paraformaldehyde.

In order to prepare the phenolic resins, a molar ratio aldehyde tophenol of at least 1.0 should be used. A molar ratio of aldehyde tophenol is preferred of at least 1:1.0, with at least 1:0.58 being themost preferable.

In order to obtain alkoxy-modified phenolic resins, primary andsecondary aliphatic alcohols are used, having an OH-group containingfrom 1 to 10 carbon atoms. Suitable primary or secondary alcoholsinclude, for example, methanol, ethanol, n-propanol, isopropanol,n-butanol, and hexanol. Alcohols with 1 to 8 carbon atoms are preferred,in particular, methanol and butanol.

The manufacture of alkoxy-modified phenolic resins is described forexample in EP-B-0 177 871. They can be manufactured using either aone-step or a two-step process. With the one-step-process, the phenoliccomponents, the aldehyde and the alcohol are brought to a reaction inthe presence of suitable catalysts. With the two-step-process, anunmodified resin is first manufactured, which is subsequently treatedwith alcohol.

The ratio of alcohol to phenol influences the properties of the resin aswell as the speed of the reaction. Preferably, the molar ratio ofalcohol to phenol amounts to less than 0.25. A molar ratio of from0.18-0.25 is most preferred. If the molar ratio of alcohol to phenolamounts to more than 0.25, the moisture resistance decreases.

Suitable catalysts are divalent salts of Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb,Ca and Ba. Zinc acetate is preferred.

Alkoxylation leads to resins with a low viscosity. The resinspredominantly exhibit ortho-ortho benzyl ether bridges and furthermore,in ortho- and para-position to the phenolic OH-groups, they exhibitalkoxymethylene groups with the general formula —(CH₂O)_(n)R. In thiscase R is the alkyl group of the alcohol, and n is a small whole numberin the range of 1 to 5.

All solvents, which are conventionally used in binder systems in thefield of foundry technology, can be used. It is even possible to usearomatic hydrocarbons in large quantities as essential elements in thesolution, except that those solvents are not preferred because ofenvironmental considerations. For that reason, the use of oxygen-rich,polar, organic solvents are preferred as solvents for the phenolic resincomponents. The most suitable are dicarboxylic acid ester, glycol etherester, glycol diester, glycol diether, cyclic ketone, cyclic ester(lactone) or cyclic carbonate.

Cyclic ketone and cyclic carbonate are preferred. Dicarboxylic acidester exhibits the formula R₁OOC—R₂—COOR₁, where the R₁, independentlyfrom one another, represent an alkyl group with 1-12, and preferably 1-6carbon atoms, and R₂ is an alkylene group with 1-4 carbon atoms.Examples are dimethyl ester from carboxylic acids with 4 to 6 carbonatoms, which can, for example, be obtained under the name “dibasicester” from DuPont.

Glycol ether esters are binders with the formula R₃—O—R₄—OOCR₅, where R₃represents an alkyl group with 1-4 carbon atoms, R₄ is an alkylene groupwith 2-4 carbon atoms, and R₅ is an alkyl group with 1-3 carbon atoms(for example butyl glycolacetate), with glycol etheracetate beingpreferred. Glycol diesters exhibit the general formula R₅COO—R₄—OOCR₅where R4 and R₅ are as defined above and the remaining R₅ are selected,independently of each other (for example, propyleneglycol diacetate),with glycol diacetate being preferred.

Glycol diether is characterized by the formula R₃—O—R₄—O—R₃, where R₃and R₄ are as defined above and the remaining R₃ are selectedindependent of each other (for example, dipropyleneglycol dimethylether). Cyclic ketone, cyclic ester and cyclic carbonate with 4-5 carbonatoms are likewise suitable (for example, propylene carbonate). Thealkyl- and alkylene groups can be branched or unbranched.

These organic polar solvents can preferably be used either asstand-alone solvents for the phenolic resin or in combination with fattyacid esters, where the content of oxygen-rich solvents in a solventmixture should predominate. The content of oxygen-rich solvents ispreferably at least 50% by weight, more preferably at least 55% byweight of the total solvents.

Reducing the content of solvents in binder systems can have a positiveeffect on the development of smoke. Whereas conventional phenolic resinsgenerally contain around 45% by weight and, sometimes, up to 55% byweight of solvents, in order to achieve an acceptable process viscosity(of up to 400 mPa·s), the amount of solvent in the phenolic-componentcan be restricted to at most 40% by weight, and preferably even 35% byweight, through the use of the low viscosity phenolic resins describedherein, where the dynamic viscosity is determined by the Brookfield HeadSpindle Process.

If conventional non alkoxy-modified phenolic resins are used, theviscosity with reduced quantities of solvent lies well outside therange, which is favorable for technical applications of up to around 400mPa·s. In some parts, the solubility is also so bad that at roomtemperature phase separation can be observed. At the same time theimmediate strength of the cores manufactured with this binder system isvery low.

Suitable binder systems exhibit an immediate strength of at least 150N/cm² when 0.8 parts by weight each of the phenolic resin and isocyanatecomponent are used for 100 parts by weight of an aggregate, like, forexample, Quarzsand H32 (see for instance EP 771 599 or DE 43 27 292).

The addition of fatty acid ester to the solvent of the phenoliccomponent leads to especially good release properties. Fatty acids aresuitable, such as, for example, those with 8 to 22 carbons, which areesterified with an aliphatic alcohol. Usually fatty acids with a naturalorigin are used, like, for example, those from tall oil, rapeseed oil,sunflower oil, germ oil, and coconut oil. Instead of the natural oils,which are found in most mixtures of various fatty acids, single fattyacids, like palmitic fatty acid or myristic fatty acid can, of course,be used.

Aliphatic mono alcohols with 1 to 12 carbons are particularly suitablefor the esterification of fatty acids. Alcohols with 1 to 10 carbonatoms are preferred, s with alcohols with 4 to 10 carton atoms beingespecially preferred. Based on the low polarity of fatty acid esters,whose alcohol components exhibit 4 to 10 carbon atoms, it is possible toreduce the quantity of fatty acid esters, and to reduce the buildup ofsmoke. A line of fatty acid esters is commercially obtainable.

Fatty acid esters, whose alcohol components contain from 4 to 10 carbonatoms, are especially advantageous, since they also give binder systemsexcellent release properties, when their content in the solventcomponent of the phenolic component amounts to less than 50% by weightbased upon the total amount of solvents in the phenolic resin component.As examples of fatty acid esters with longer alcohol components, are thebutyl esters of oleic acids and tall oil fatty acid, as well as themixed octyl-decylesters of tall oil fatty acids.

By using the alkoxy-modified phenolic resins described herein, aromatichydrocarbons can be avoided as solvents for the phenolic component. Thisis because of the excellent polarity of the binders. Oxygen-richorganic, polar solvents, can now be used as stand-alone solvents.Through the use of the alkoxy-modified phenolic resins, the quantity ofsolvents required can be restricted to less than 35% by weight of thephenolic component. This is made possible by the low viscosity of theresins. The use of aromatic hydrocarbons can, moreover, be avoided.

The use of the binder systems with at least 50% by weight of the abovenamed oxygen-rich, polar, organic solvents as components in the solventsof the phenolic components leads, moreover, to a doubtlessly lowerdevelopment of smoke, in comparison with conventional systems with ahigh proportion of fatty acid esters in the solvent.

The two components of the binder system include an aliphatic,cycloaliphatic or aromatic polyisocyanate, preferably with 2 to 5isocyanate groups. Based on the desired properties, each can alsoinclude mixtures of organic isocyanates. Suitable polyisocyanatesinclude aliphatic polyisocyanates, like, for example,hexamethylenediisocyanate, alicyclic polyisocyanates like, for example,4,4′-dicyclohexylmethanediisocyanate, and dimethyl derivates thereof.

Examples of suitable aromatic polyisocyanates aretoluol-2,4-diisocyanate, toluol-2,6-diisocyanate,1,5-napththalenediisocyanate, triphenylmethane-triisocyanate,xylylenediisocyanate and its methyl derivatives, polymethylenepolyphenylisocyanate and chlorophenylene-2,4-diisocyanate. Preferredpolyisocyanates are aromatic polyisocyanates, in particular,polymethylenepolyphenyl polyisocyanates such as diphenylmethanediisocyanate.

In general 10-500% by weight of the polyisocyanates compared to theweight of the phenolic resins are used. 20-300% by weight of thepolyisocyanates is preferred. Liquid polyisocyanates can be used inundiluted form, whereas solid or viscous polyisocyanates can bedissolved in organic solvents. The solvent can consist of up to 80% byweight of the isocyanate components.

As solvents for the polyisocyanate, either the above-named fatty acidesters or a mixture of fatty acid esters and up to 50% by weight ofaromatic solvents can be used. Suitable aromatic solvents arenaphthalene, alkyl-substituted naphthalenes, alkyl-substituted benzenes,and mixtures thereof.

Especially preferred are aromatic solvents, which consist of mixtures ofthe above named aromatic solvents and which have a boiling point rangeof between 140 and 230° C. However, preferably no aromatic solvents areused.

Preferably, the amount of polyisocyanate used results in the number ofthe isocyanate group being from 80 to 120% with respect to the number ofthe free hydroxyl group of the resin.

In addition to the already mentioned components, the binder systems caninclude one or more conventional additives, like, for example, thosechosen from among silanes (see for instance U.S. Pat. No. 4,540,724),drying oils (U.S. Pat. No. 4,268,425) or “Komplexbildner” (WO 95/03903).

The binder systems are offered, preferably, as two-component-systems,whereby the solution of the phenolic resin represents one component andthe polyisocyanate, also in solution, if appropriate, is the othercomponent. Both components are combined and subsequently mixed with sandor a similar aggregate, in order to produce the moulding compound. Themoulding compound contains an effective binding quantity of up to 15% byweight of the binder system with respect to the weight of the aggregate.

It is also possible to subsequently mix the components with quantitiesof sand or aggregates and then to join these two mixtures. Processes forobtaining a uniform mixture of components and aggregates are known tothe expert. In addition, if appropriate, the mixture can contain otherconventional ingredients, like iron oxide, ground flax fiber, xylem,pitch and refractory meal (powder).

In order to manufacture foundry-moulded pieces from sand, the aggregateshould exhibit a sufficiently large particle size. In this way, thefounded piece has sufficient porosity, and fugitive gasses can escapeduring the casting process. In general at least 80% by weight andpreferably 90% by weight of the aggregate should have an averageparticle size of less than or equal to 290 μm. The average particle sizeof the aggregate should be between 100 μm and 300 μm.

For standard-founded pieces, sand is preferred as the aggregate materialto be used, where at least 70% by weight, and preferably more than 80%by weight of the sand is silicon dioxide. Zircon, olivine,aluminosilicate sands and chromite sands are likewise suitable asaggregate materials.

The aggregate material is the main component in founded pieces. Infounded pieces from sand for standard applications, the proportion ofbinder in general amounts to up to 15% by weight, and often between 0.5%and 7% by weight, with respect to the weight of the aggregate.Especially preferred is 0.6% to 5% by weight of binder compared to theweight of the aggregate.

Although the aggregate is primarily added dry, up to 0.1% by weight ofmoisture can be tolerated, with respect to the weight of the aggregate.The founded piece is cured so that it retains its exterior shape afterbeing removed from the mold.

In a preferred implementation, silane with the general formula therefore—(R′—O)₃—Si—R— is added to the moulding compound before the curingbegins. Here, R′ is a hydrocarbon radical, preferably an alkyl radicalwith 1-6 carbon atoms, and R is an alkyl radical, an alkoxy-substitutedalkyl radical or an alkyl amine-substituted amine radical with alkylgroups having 1-6 carbon atoms. The addition of from 0.1% to 2% byweight with respect to the weight of the binder system and catalysts,reduces the moisture sensitivity of the system.

Examples of commercially obtainable silanes are Dow Coming Z6040 andUnion Carbide A-187 (γ-glycidoxypropyltrimethoxysilane), Union CarbideA-1100 (γ-aminopropyl triethoxysilane), Union Carbide A-1120(N-β-(aminoethyl)-γ-amino-propyltrimethoxysilane) and Union CarbideA1160 (ureidosilane).

If applicable, other additives can be used, including wetting agents andsand mixture extending additives (English Benchlife-additives), such asthose disclosed in U.S. Pat. No. 4,683,252 or U.S. Pat. No. 4,540,724.In addition, mould release agents like fatty acids, fatty alcohols andtheir derivatives can be used, but as a rule, they are not necessary.

The curing of the founded piece (i.e. binder+aggregate) is carried outunder conditions well known in the art, using, as catalytic system, ablend of at least two tertiary amines as hereinbefore described.

The present invention also relates to a process of casting a metal, saidprocess comprises:

-   -   a) preparing a foundry shape as described above in steps (a) to        (e),    -   b) pouring said metal while in the liquid state into a round        said shape;    -   c) allowing said metal to cool and solidify; and    -   d) then separating the molded article from the foundry shape.

The invention is now further illustrated by the following examples,which are not intented to bring any limitation to the present invention.

EXAMPLES

A test was firstly carried out for the measurement of the optimized,i.e. minimum amount of, amine quantity of a single tertiary amine (DMEA,DEMA or DMIPA) or a blend of tertiary amines (DMEA-DEMA, DMEA-TEA) forfull curing in order to show the difference of reactivity.

The various resins used for this test are commercial resins fromAshland-Avébène (Usine du Goulet—20, rue Croix du Vallot, 27600 StPierre-la-Garenne, France) sold under the trade name Avecure®; theseresins are composed of a formo-phenolic resin and of an isocyanateresin, in accordance with the present description.

The catalytic behaviour of the tertiary amines in polyurethane curing isassessed for each any resin: full curing of a 1.870-1.880 kg cylinder(length 300 mm×diameter 70 mm) of sand LA32+binder requires about0.2-0.4 mL of DMEA, while it requires up to almost 1 mL of DEMA and canrequire up to about 1.5 mL of TEA. While using blends of DMEA-DEMA orDMEA-TEA, the following results are obtained:

Example 1 Blends of DMEA/DEMA

A fixed amount of sand+resins mixture with a predetermined amount ofresins per mass unit of sand (normally between 0.5 and 2% by weight ofeach resin based on the amount of sand mixed) is placed in a longcylindrical shaped mould, the amine is poured as liquid ahead of thesand-resins cylinder in a U tube and a heated stream of carrier gas(normally nitrogen) at a fixed and predetermined rate is passed throughthe amine loaded U tubing.

The carrier gas stream brings the volatilized amine to the cylinderfilled with sand+binder during a fixed time. Test cores were prepared asfollows:

Into a laboratory mixer, 0.8 part by weight of the phenolic resinsolution and 0.8 part by weight of the polyisocyanate solution are addedto 100 parts by weight of sand LA32 (Silfraco), in the order given, andmixed intensively for 3 minutes. 6 kg of fresh sand are used for eachresin to be cured. This quantity allows 3 gassings of 1.870-1.880 kg ofsand+binder for repeatability sake.

The 3 gassings are made at 5.5 bars (static) equivalent to 4.8 bars(dynamic). 2 purgings of 10 seconds each are applied between eachgassing operation. Gassing itself lasts 10 seconds at 1.5 bars(dynamic). Carrier gas heater is adjusted to 75° C.±3° C. except for TEAfor which it was modified to 95° C.

The optimum (lowest) volume for 100% curing for each amine or blend ofamine is obtained by increasing the volume of injected amine(s) by stepsof 0.05 mL from 0, until reaching the catalytic volume for which no moresand is left free (100% curing, the sand+binder test core is totallysolidified).

Amine(s) optimized volumes have been converted to weights required forfull curing through usage of their corresponding densities. The aminesdensity was measured or checked from literature on a densimeter MetierToledo DA-100M. The density of DMEA is 0.678, the one of DEMA is 0.706,density of TEA is 0.728.

The checking of density value of blends versus the predicted one basedon linear combination of individual density of each amine of thecomposition have shown that no volume contraction intervenes that couldhave accounted for lower volumes than expected at application.

Table 1 indicates the amounts (in grams) of single tertiary amine (DMEAor DEMA) and the amount of different DMEA/DEMA blends required for afull curing core test as described above. Theoretical masses (Theo.Mass) of blends needed for 100% test core curing in Table 1 arecalculated according to the s following equation:

Theo Mass=(ratio of DMEA×mass of DMEA alone needed for full curing+ratioof DEMA×mass of DEMA alone needed for full curing).

TABLE 1 Type of Resin Avecure ® Avecure ® Avecure ® Amine 333/633331/631 363/663 Mass of DMEA required for 100% curing 0.3051 0.3390.2034 Mass of DEMA required for 100% curing 0.5656 0.777 0.31815Experimental Mass of 50/50 DMEA/DEMA blend 0.38115 0.4158 0.2079Theoretical Mass of 50/50 DMEA/DEMA blend 0.43535 0.55835 0.260775Experimental Mass of 20/80 DMEA/DEMA blend 0.3861 0.5967 0.2808Theoretical Mass of 20/80 DMEA/DEMA blend 0.5135 0.68996 0.2952Experimental Mass of 10/90 DMEA/DEMA blend 0.45825 0.6345 0.282Theoretical Mass of 10/90 DMEA/DEMA blend 0.53955 0.73383 0.306675

From the results of Table 1, it can be easily seen that a blend ofDMEA-DEMA containing 10, 20 or 50% of DMEA is more reactive than DEMAalone, as seen by lower quantities requested for full curing in the caseof blends. is [0101] The results given in Table 1 also indicate that for10/90, 20/80 and 50/50 blends of DMEA/DEMA, the required global amountof amines for full curing the test core is lower that the scheduled onebased on single amines, i.e. (ratio of DMEA x mass (g) of DMEA aloneneeded for full curing+ratio of DEMA×mass (g) of DEMA alone needed forfull curing).

Example 2 Blends of DMEA/TEA

Theoretical masses (Theo. Mass) of blends needed for 100% test corecuring are calculated according to the following equation:

Theo Mass=(ratio of DMEA×mass of DMEA alone needed for full curing+ratioof TEA×mass of TEA alone needed for full curing).

Table 2 indicates the amount of single tertiary amine (DMEA or TEA) andthe amount of different DMEA/TEA blends required for a full test corecuring as described above.

TABLE 2 Amine Experimental Theoretical Mass (g) of Mass (g) of mass (g)of mass (g) of DMEA TEA required 20/80 20/80 required for for 100%DMEA/TEA DMEA/TEA Resin 100% curing curing blend blend Avecure ® 0.37290.9464 0.612 0.8317 373/673 Avecure ® 0.3051 1.456 0.936 1.22582 353/653Avecure ® 0.3051 1.456 0.792 1.22582 333/633 Avecure ® 0.339 1.456 0.9361.2326 331/631 Avecure ® 0.2034 0.9464 0.36 0.7978 363/663

The results of Table 2 show that quantities of the 20/80 DMEA/TEA blendneeded for a full curing of the test core are lower than the quantity ofTEA alone needed for a 100% curing.

The results of Table 2 also show that quantities of the 20/80 DMEA/TEAblend needed for a full curing of the test core are lower thantheoretical amounts of the 20/80 DMEA/TEA blend as calculated by addingproportionally the optimized quantities of individual amines when usedalone.

1. Use of a blend of at least two tertiary amines as catalyst for curinga composite resin composition.
 2. Use according to claim 1, for curing afoundry shape by the cold box process.
 3. Use according to any of claim1 or 2, wherein each amine is present in the blend in an amount of notless than 10% by weight, and not more than 90% by weight.
 4. Useaccording to any of claims 1 to 3, wherein the blend comprises at leastone tertiary amine having 3 to 5 carbon atoms with at least one tertiaryamine having 6 to 10 carbons.
 5. Use according to any of claims 1 to 4,wherein the amines are chosen from trimethylamine, N-methylaziridine,dimethylethylamine (DMEA), N-methylazetidine, N-ethylaziridine,diethylmethylamine (DEMA), dimethyl-isopropylamine (DMIPA),dimethyl-n-propylamine (DMPA), N-n-propylaziridine,N-iso-propylaziridine, N-ethylazetidine, N-methylpyrrolidine,N,N,N′,N′-tetramethyl diamino methane, triethylamine (TEA),methylethyl-n-propylamine, methylethyl-iso-propylamine,dimethyl-n-butylamine, dimethyl-sec-butylamine, dimethyl-iso-butylamine,dimethyl-tert-butylamine, N-ethylpyrrolidine, N-methylpiperidine,hexamethylene tetramine, dimethyl piperazine, N,N,N′,N′-tetramethyldiamino ethane, dimethylpentylamines, methylethylbutylamines,diethylpropylamines, dipropylmethylamines, N-propylpyrrolidines,N-ethylpiperidine, dimethyl hexylamines, methylethylpentylamines,diethylbutylamines, dipropylethylamines, N-butylpyrrolidines,N-propylpiperidines, diethyl piperazine, dimethyiheptylamines,methylethylhexylamines, diethylpentylamines, tripropylamines,N-pentylpyrrolidines, N-butylpiperidines, dimethyloctylamines,methylethyl heptylamines, diethylhexylamines, ethylpropylpentylamines,dipropylbutylamines and N-pentylpiperidines.
 6. Use according to any ofclaims 1 to 5, wherein the amines are chosen from DMEA, DMIPA, DEMA,DMPA and TEA.
 7. Use according to any of claims 1 to 6, wherein theblend of amines are chosen from DMEA-DMIPA, DMEA-DEMA, DMEA/DMPA andDMEA-TEA.
 8. Use according to any of claims 1 to 7, wherein the blend ofamines are chosen from 50/50 DMEA/DMIPA, 20/80 DMEA/DMIPA, 10/90DMEA/DMIPA, 50/50 DMEA/DMPA, 20/80 DMEA/DMPA, 10/90 DMEA/DMPA, 50/50DMEA/DEMA, 20/80 DMEA/DEMA, 10/90 DMEA/DEMA, 50/50 DMEA/TEA, 20/80DMEA/TEA, 10/90 DMEA/TEA, 80/20 DMEA/TEA and 90/10 DMEA/TEA, ispreferably 20/80 DMEA/DMIPA, 20/80 DMEA/TEA and 80/20 DMEA/TEA. 9.Process for preparing a foundry shape by the cold box process, whichprocess comprises the following steps: (a) forming a foundry mix withthe binder and an aggregate, (b) forming a foundry shape by introducingthe foundry mix obtained from step (a) into a pattern, (c) contactingthe shaped foundry mix with a curing catalyst comprising a blend of atleast two tertiary amines according to any of claims 1 to 8, in a liquidor preferably in a gaseous form, optionally with an inert carrier, (d)hardening the aggregate-resins mix into a hard, solid, cured shape, and(e) removing the hardened foundry shape of step (d) from the pattern.10. Process according to claim 9, wherein the inert gaseous carrier isnitrogen, air, and/or carbon dioxide.
 11. Process according to claim 9or 10, wherein the curing catalyst system is a mixture comprising, inaddition to the blend of at least two tertiary amines, up to 25%,preferably up to 10% and advantageously up to 0.5% by weight of at leastanother amine, primary and/or secondary.
 12. Process according to any ofclaims 9 to 11, wherein the curing catalyst system contains 0.2% byweight of water.
 13. Process according to any of claims 9 to 12, whereinthe blend is a mixture of at least one tertiary amine having 3 to 5carbon atoms with at least one tertiary amine having 6 to 10 carbons.14. Process according to any of claims 9 to 13, wherein the blend ischosen from DMEA-DMIPA, DMEA-DEMA, DMEA/DMPA and DMEA-TEA.
 15. Processaccording to any of claims 9 to 13, wherein the blend is chosen from50/50 DMEA/DMIPA, 20/80 DMEA/DMIPA, 10/90 DMEA/DMIPA, 50/50 DMEA/DMPA,20/80 DMEA/DMPA, 10/90 DMEA/DMPA, 50/50 DMEA/DEMA, 20/80 DMEA/DEMA,10/90 DMEA/DEMA, 50/50 DMEA/TEA, 20/80 DMEA/TEA, 10/90 DMEA/TEA, 80/20DMEA/TEA and 90/10 DMEA/TEA, preferably 20/80 DMEA/DMIPA, 20/80 DMEA/TEAand 80/20 DMEA/TEA.
 16. Process for making a core or a mold comprisingin addition to the process as defined in anyone of claims 9 to 14 afurther step of hardening the hardened foundry shape obtained from step(e).
 17. Process of casting a metal, characterised in that it comprisesthe following steps: a) preparing a foundry shape in accordance withanyone of claims 9 to 15, b) pouring said metal while in the liquidstate into a round said shape; c) allowing said metal to cool andsolidify; and d) then separating the molded article.